/Engine/Source/Runtime/SlateCore/Public/Containers/ObservableArray.h
Valid for the Add, Remove, RemoveSwap action. UseGetItems.Num()to know how many elements were added/removed. Add: The array index where we added the elements. Remove: The old array index before it removed the elements. The index is not valid anymore. RemoveSwap: The old array index before it removed the elements. The index is valid if the array is not empty.
The index the action started.
SizeType GetActionIndex() const